First Vertebrates Evolved in Shallow Water

Fish stuck to coastal habitats for nearly 100 million years after they first appeared.

Oct 25, 2018

Kerry Grens

ABOVE: Pituriaspis, a jawless fish that lived 410 million years agoNOBUMICHI TAMURA

The paucity of fossils from the time of the earliest vertebrates—around 480 million years ago—has made it hard to definitively determine the types of habitats where backbones first evolved. But predictions based on the fossil data that do exist suggest all the various forms of the first vertebrates, from jawless fish to bony fish, originated in shallow environments near shore, researchers report today (October 25) in Science.

Catalina Pimiento, a paleobiologist at Swansea University in Wales who was not part of the study, tells Science News that the result makes sense. “It’s just well-known that these coastal habitats [have supported] biodiversity.”

The team that did the study gathered fossil data from around 2,800 specimens ranging from 480 million to 360 million years ago. Combining those records with environmental information, the paleontologists developed a model revealing that time and again vertebrate clades got their starts in intertidal and subtidal zones. What’s more is that those animals stuck around for about 100 million years before spreading into new territory.

The conclusion helps explain the incomplete fossil record, the authors write in their report. Waves near the shore might have battered fossils, resulting in the tiny fragments that make up much of the preserved gnathostome specimens from the Ordovician period roughly 440 million to 480 million years ago.

The study raises questions related to modern-day nearshore habitats. “One of the things we want to know is whether these shallow waters are still the biological pump that is feeding the reef,” Lauren Sallan, a paleobiologist at the University of Pennsylvania and study coauthor, says in a press release. “Where is the current site of innovation?”